The present invention relates to a system for controlling the fuel injection of an automotive engine in dependence on a throttle opening degree and engine speed.
Japanese Patent Application Laid Open No. 55-32913 discloses a fuel injection system wherein a basic fuel injection pulse width Tp is calculated in dependence on throttle opening degree .alpha. and engine speed Ne. The basic pulse width Tp are stored in a table and are derived from the table for controlling the fuel injection during the operation of the engine.
However, since there is a space between the throttle valve and a cylinder of the engine, such as a chamber formed downstream of the throttle valve, changing of actual amount of induced air per engine cycle in response to the change of the throttle opening degree during the transient state is delayed. Accordingly, when the throttle valve is rapidly opened, the air-fuel mixture becomes rich. To the contrary, when the throttle valve is rapidly closed, the air-fuel mixture becomes lean.
Referring to FIG. 5 showing an increase in quantity of intake air at an acceleration of a vehicle, the basic fuel injection pulse width is determined dependent on air quantity M.sub.0 which is calculated based on the opening degree .alpha. of a throttle and engine speed detected at a point A before an induction stroke of a cylinder, for example No. 1 cylinder. However, an actual air quantity M.sub.1 at a point B after the induction stroke is larger than the quantity M.sub.0 because of air induction at the induction stroke. Thus, there is a difference .DELTA.M between the estimated quantity M.sub.0 and the actual quantity M.sub.1. As a result, the air-fuel ratio fluctuates at a transient state.
In a system disclosed in Japanese Patent Application Laid Open No. 60-43135, a necessary air flow is estimated dependent on the depressing degree of an accelerator pedal and engine speed. The fuel injection quantity is determined taking account of a first order lag of the actual air flow. Accordingly, fuel is gradually increased until the actual air flow coincides with the necessary air flow. However, the estimation of the air flow is inaccurate so that the air-fuel ratio of the fuel mixture fluctuates.